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A quick recap on gases !!!

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- 1. GASEOUS STATE
- 2. TYPES Basically we observe with 3 states of matter namely SOLIDS LIQUIDS & GASES
- 3. LET’S See …
- 4. Apart from the 3 states of matter, there are 2 more states of matter Plasma Bohr-Einstein Condensate Plasma is not a common state of matter on the earth , but a common one among stars which produces that excessive heat & light.That means plasma matter has high kinetic energies.
- 5. In contrast to this , Bohr-Einstein condensate(BEC) has very low & even zero kinetic energies. Due to this zero kinetic energies atoms loose their molecular motions & begin to clump together and form condensates named BEC’s. We have to make a note that kinetic energies are directly proportional to absolute temperatures & hence BEC’s also would form & exist at extremely low temperatures.
- 6. GASES As we all know the properties of gases or the gas mixtures .. The formost property is DIFFUSION of GASES Diffusion is the movement of gases from a region of higher concentration to a region of lower concentration which is exactly opposite to OSMOSIS which is a property of liquids. Now this diffusion of gases is measured in terms of rates of diffusion.
- 7. Rate of Diffusion(r) The volume of a gas that diffuses in unit time is said to be rate of diffusion (r) of a gas . r=V/t or r1/r2 = V1/V2 * t2/t1 if the two gases have equal volumes then , r1/r2 = t2/t1
- 8. EFFUSION Similar to diffusion , EFFUSION is also a property of gases Effusion is defined as the movement of gases from a region of higher concentration to that of lower concentration through a small pore. The best example of effusion are like… 1) Escape of air from balloon 2) Escape of air from punctured cycle tube. 3) Gas leakages from pipes / cylinders
- 9. GAS LAWS A very imp. arena of this chapter is on gas laws. Here we shall deal with 5 gas laws…. 1) Boyle ‘s law 2) Charles law 3) Avogadros law 4) Grahams law of Diffusion 5) Dalton’s law Lets see one by one in detail……
- 10. PV = K Boyle’s law The pressure of a given mass of gas is inversly proportional to volume at constant temperature. or
- 11. A graph drawn for Boyles law is shown as Pressure vs Volume P V
- 12. If a graph of boyles law is drawn between P vs 1/V , That is represented as P 1/V
- 13. Similarly if a graph is drawn among PV vs P is given as PV P
- 14. Charles laws Statement 1 Charles law -1 1 states that , at constant pressure for every one degree rise in temperature , the volume of a given mass of gas changes by 1/273 of its volume at ‘0’ degrees centigrade. Vt= V0 1+ t/273
- 15. Charles law-1 graph A graph plotted for statement 1 of charles law is shown as V m v0 0 T
- 16. Statement - 2 It states that at constant volume , pressure of a given mass of gas is directly proportional to temperature or At constant pressure, volume of a given mass of gas is directly proportional to temperature . V T or P T V=KT P=KT V1/V2=T1/T2 P1/P2=T1/T2
- 17. Graphical representation The graphs drawn for charles law 1 & 2 are given as V3 P3 V2 P2 P1 V1 V P T T
- 18. AVOGADRO’S law Equal volumes of all gases contain equal number of molecules under similar conditions of temperature and pressure. & or or V n V=nK V/n = K V1/n1=V2/n2 V1n2=V2n1
- 19. IDEAL GAS EQUATION From the 3 gas laws , studied till now … ideal gas equation can be derived as follows PV=K ……… eq 1 P=KT ……... eq 2 V= nK ………. eq 3 From 1,2 & 3 PV=nKT Replacing constant K, with Universal gas Constant we get PV=nRT
- 20. Values of ‘R’ NUMERICAL VALUE UNITS 8.314 Joules 0.08206 L.atm 1.987 Calories 62.36 L.torr 82.1 atm.cc
- 21. GRAHAMS LAW OF DIFFUSION Grahams law of diffusion states that the rate of diffusion of a gas is inversly proportional to the squareroot of density or molecular weight.
- 22. DALTONS LAW It states that , at constant temperature the total pressure of a gas in a gaseous mixture is the sum of partial pressures of the gases. P= p1+p2+p3+…….. At const. ‘T’ ; the partial pressure of a gas is directly proportional to its molefraction (
- 23. Kinetic gas Equation The kinetic gas equation is given as PV=1/3 mnc2
- 24. Types of velocities Gas molecules exhibit with three different kinds of velocities … 1) Average velocity ( C ) 2) Most probable velocity ( C p ) 3) Root meansquare velocity ( C rms )
- 25. Ratio of velocities The ratio of C p , C & Crms can be given as 1:1.128 : 1.223
- 26. INTERMOLECULAR FORCES vs THERMAL ENERGY Inter molecular forces are forces which mediate interraction between molecules; be it forces of attraction or forces of repulsion. These intermolecular forces of attraction are cheifly studied as hydrogen bonding , dipole forces of attraction. Thermal energy is the average kinetic energy of the molecules of a substance. Thermal energy is a very key factor for the liquifaction of gases.
- 27. Physical state of a substance always depends on the extent of intermolecular forces & thermal energy.
- 28. REAL GAS vs IDEAL GAS Gases which follow ideal gas equation i.e PV=nRT are said to be ideal gases & Gases which donot follow ideal gas equation are said be real gases. And in general , all gases are real & no gas is ideal. The reason behind real behaviour of gases are 1) Molecules of a gas donot exhibit any forces of attraction among them. 2) Volume of gas occupied is negligibly small wrt space occupied by the gas.
- 29. GRAPHICAL NOTE CO CH4 H2 He PV P Real gas ideal gas Ideal gas P V
- 30. LIQUIFACTION OF GASES Ideal gases cannot be liquified.it is only a real gas that can be liquified. Gases can be liquified on cooling below their boiling points.But if the gas to be liquified is having a very low boiling point , then it cannot be liquified by cooling furthur. Hence an another technique called JOULE-THOMPSON EFFECT is to be used. Principle behind this technique is cooling of gases by expansion from high pressure to low pressure.
- 31. There are 2 key points to achieve liquifaction of gases 1) Critical temperature ( Ct ) 2) Critical pressure ( C p ) The highest temperature at which liquifaction of gases occurs first is Ct & the pressure required to liquify a gas at its critical temperature is its Cp.
- 32. THANKYOU

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